Top portion of a mattress spring core



FIG. 1 is a top plan view of a top portion of a spring core, showing my new design;

FIG. 2 is an enlarged view taken from section 2 of FIG. 1;

FIG. 3 is a side elevational view;

FIG. 4 is an enlarged view taken from section 4 of FIG. 3;

FIG. 5 is an elevational view, showing the side opposite that shown in FIG. 3;

FIG. 6 is an enlarged view taken from section 6 of FIG. 5;

FIG. 7 is an end elevational view;

FIG. 8 is an enlarged view taken from section 8 of FIG. 7;

FIG. 9 is an end elevational view showing the end opposite that shown in FIG. 7; and,

FIG. 10 is an enlarged view taken from section 10 in FIG. 9.

The broken lines are for environmental purposes only and form no part of the claimed design. 

The ornamental design for a top portion of a mattress spring core, as shown and described. 